1. Field
The following description relates to a multi-channel transmitter optical sub-assembly (TOSA) having a structure in which a plurality of light sources are mounted on one stem.
2. Description of the Related Art
Wavelength division multiplexing (WDM)-based fiber to the home (FTTH), namely, a WDM-passive optical network (WDM-PON), is a scheme in which communication is made between a central base station and a subscriber using a wavelength allocated to each subscriber. Such a scheme is independently used by each subscriber, provides a large-scale communication service, has an excellent security, and is differentiated from a time division multiplexing (TDM) scheme in that modulation and demodulation of a light source are performed for only one subscriber.
An essential element for establishing an optical communication system is a TOSA. Generally, in the TOSA, one light source is mounted on one package to output light, and thus, TOSAs equal to the number of channels are required for configuring a multichannel system. For this reason, the system cost is high, and a consumption space is large. Such limitations occur in a TOSA using a distributed feedback laser diode (DFB-LD) or a Fabry-Perot laser diode (FP-LD).
To overcome such limitations, there is an example in which a hybrid optical transceiver module disclosed in Korean Patent Registration No. 10-0825728 was proposed. According to the example, the hybrid optical transceiver module is configured with a first package having a TOSA structure and a second package having a planar lightwave circuit (PLC) platform structure.
The first package includes a laser diode that outputs a transmission optical signal. The second package includes: a photodiode that receives a reception optical signal input through an optical fiber; an optical waveguide that transfers the transmission optical signal, emitted from the first package, to the optical fiber; and a wavelength division multiplex coupler that transfers the reception optical signal to the photodiode, and divides a transmission high-output optical signal and the reception optical signal.
The optical transceiver module can provide a multichannel light source in one package, but have a great volume because the use of the PLC is needed. Also, the optical transceiver module is required to multiplex one optical waveguide using the wavelength division multiplex coupler, causing a great loss.
To package multiple light sources into one TOSA, the number of pins for injecting a current and controlling a temperature should be sufficient. For example, eight pins (two anode pins and two cathode pins for each channel, namely, a total of eight pins) for injecting a current, two temperature control pins using a thermo-electric cooler (TEC), and two temperature monitoring pins, namely, a total of twelve pins, are needed for packaging a four-channel light source into one TOSA.
In this case, since the number of pins is large, a butterfly-type package is generally used for packaging pins into one TOSA. For this reason, a volume of the package is great. Also, when a laser diode that vertically outputs light to the package is used, it is difficult to package. For another example, in a quad small form-factor pluggable (QSFP) optical module, since signal lines are separately allocated, it is unable to package in a transistor outline-stem (TO-stem) structure.
A TO-can type package may be used for reducing a volume of a multi-channel light source, but in this case, the number of pins is insufficient. To overcome such a limitation, a pin which is used in common may be designated, but when the pin which is used in common corresponds to a signal line, crosstalk can occur.